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package java.util.logging;

/**
 * <tt>Handler</tt> that buffers requests in a circular buffer in memory.
 * <p>
 * Normally this <tt>Handler</tt> simply stores incoming <tt>LogRecords</tt>
 * into its memory buffer and discards earlier records.  This buffering
 * is very cheap and avoids formatting costs.  On certain trigger
 * conditions, the <tt>MemoryHandler</tt> will push out its current buffer
 * contents to a target <tt>Handler</tt>, which will typically publish
 * them to the outside world.
 * <p>
 * There are three main models for triggering a push of the buffer:
 * <ul>
 * <li>
 * An incoming <tt>LogRecord</tt> has a type that is greater than
 * a pre-defined level, the <tt>pushLevel</tt>. </li>
 * <li>
 * An external class calls the <tt>push</tt> method explicitly. </li>
 * <li>
 * A subclass overrides the <tt>log</tt> method and scans each incoming
 * <tt>LogRecord</tt> and calls <tt>push</tt> if a record matches some
 * desired criteria. </li>
 * </ul>
 * <p>
 * <b>Configuration:</b>
 * By default each <tt>MemoryHandler</tt> is initialized using the following
 * <tt>LogManager</tt> configuration properties where <tt>&lt;handler-name&gt;</tt>
 * refers to the fully-qualified class name of the handler.
 * If properties are not defined
 * (or have invalid values) then the specified default values are used.
 * If no default value is defined then a RuntimeException is thrown.
 * <ul>
 * <li>   &lt;handler-name&gt;.level
 * specifies the level for the <tt>Handler</tt>
 * (defaults to <tt>Level.ALL</tt>). </li>
 * <li>   &lt;handler-name&gt;.filter
 * specifies the name of a <tt>Filter</tt> class to use
 * (defaults to no <tt>Filter</tt>). </li>
 * <li>   &lt;handler-name&gt;.size
 * defines the buffer size (defaults to 1000). </li>
 * <li>   &lt;handler-name&gt;.push
 * defines the <tt>pushLevel</tt> (defaults to <tt>level.SEVERE</tt>). </li>
 * <li>   &lt;handler-name&gt;.target
 * specifies the name of the target <tt>Handler </tt> class.
 * (no default). </li>
 * </ul>
 * <p>
 * For example, the properties for {@code MemoryHandler} would be:
 * <ul>
 * <li>   java.util.logging.MemoryHandler.level=INFO </li>
 * <li>   java.util.logging.MemoryHandler.formatter=java.util.logging.SimpleFormatter </li>
 * </ul>
 * <p>
 * For a custom handler, e.g. com.foo.MyHandler, the properties would be:
 * <ul>
 * <li>   com.foo.MyHandler.level=INFO </li>
 * <li>   com.foo.MyHandler.formatter=java.util.logging.SimpleFormatter </li>
 * </ul>
 * <p>
 *
 * @since 1.4
 */

public class MemoryHandler extends Handler {

  private final static int DEFAULT_SIZE = 1000;
  private volatile Level pushLevel;
  private int size;
  private Handler target;
  private LogRecord buffer[];
  int start, count;

  // Private method to configure a MemoryHandler from LogManager
  // properties and/or default values as specified in the class
  // javadoc.
  private void configure() {
    LogManager manager = LogManager.getLogManager();
    String cname = getClass().getName();

    pushLevel = manager.getLevelProperty(cname + ".push", Level.SEVERE);
    size = manager.getIntProperty(cname + ".size", DEFAULT_SIZE);
    if (size <= 0) {
      size = DEFAULT_SIZE;
    }
    setLevel(manager.getLevelProperty(cname + ".level", Level.ALL));
    setFilter(manager.getFilterProperty(cname + ".filter", null));
    setFormatter(manager.getFormatterProperty(cname + ".formatter", new SimpleFormatter()));
  }

  /**
   * Create a <tt>MemoryHandler</tt> and configure it based on
   * <tt>LogManager</tt> configuration properties.
   */
  public MemoryHandler() {
    sealed = false;
    configure();
    sealed = true;

    LogManager manager = LogManager.getLogManager();
    String handlerName = getClass().getName();
    String targetName = manager.getProperty(handlerName + ".target");
    if (targetName == null) {
      throw new RuntimeException("The handler " + handlerName
          + " does not specify a target");
    }
    Class<?> clz;
    try {
      clz = ClassLoader.getSystemClassLoader().loadClass(targetName);
      target = (Handler) clz.newInstance();
    } catch (ClassNotFoundException | InstantiationException | IllegalAccessException e) {
      throw new RuntimeException("MemoryHandler can't load handler target \"" + targetName + "\"",
          e);
    }
    init();
  }

  // Initialize.  Size is a count of LogRecords.
  private void init() {
    buffer = new LogRecord[size];
    start = 0;
    count = 0;
  }

  /**
   * Create a <tt>MemoryHandler</tt>.
   * <p>
   * The <tt>MemoryHandler</tt> is configured based on <tt>LogManager</tt>
   * properties (or their default values) except that the given <tt>pushLevel</tt>
   * argument and buffer size argument are used.
   *
   * @param target the Handler to which to publish output.
   * @param size the number of log records to buffer (must be greater than zero)
   * @param pushLevel message level to push on
   * @throws IllegalArgumentException if {@code size is <= 0}
   */
  public MemoryHandler(Handler target, int size, Level pushLevel) {
    if (target == null || pushLevel == null) {
      throw new NullPointerException();
    }
    if (size <= 0) {
      throw new IllegalArgumentException();
    }
    sealed = false;
    configure();
    sealed = true;
    this.target = target;
    this.pushLevel = pushLevel;
    this.size = size;
    init();
  }

  /**
   * Store a <tt>LogRecord</tt> in an internal buffer.
   * <p>
   * If there is a <tt>Filter</tt>, its <tt>isLoggable</tt>
   * method is called to check if the given log record is loggable.
   * If not we return.  Otherwise the given record is copied into
   * an internal circular buffer.  Then the record's level property is
   * compared with the <tt>pushLevel</tt>. If the given level is
   * greater than or equal to the <tt>pushLevel</tt> then <tt>push</tt>
   * is called to write all buffered records to the target output
   * <tt>Handler</tt>.
   *
   * @param record description of the log event. A null record is silently ignored and is not
   * published
   */
  @Override
  public synchronized void publish(LogRecord record) {
    if (!isLoggable(record)) {
      return;
    }
    int ix = (start + count) % buffer.length;
    buffer[ix] = record;
    if (count < buffer.length) {
      count++;
    } else {
      start++;
      start %= buffer.length;
    }
    if (record.getLevel().intValue() >= pushLevel.intValue()) {
      push();
    }
  }

  /**
   * Push any buffered output to the target <tt>Handler</tt>.
   * <p>
   * The buffer is then cleared.
   */
  public synchronized void push() {
    for (int i = 0; i < count; i++) {
      int ix = (start + i) % buffer.length;
      LogRecord record = buffer[ix];
      target.publish(record);
    }
    // Empty the buffer.
    start = 0;
    count = 0;
  }

  /**
   * Causes a flush on the target <tt>Handler</tt>.
   * <p>
   * Note that the current contents of the <tt>MemoryHandler</tt>
   * buffer are <b>not</b> written out.  That requires a "push".
   */
  @Override
  public void flush() {
    target.flush();
  }

  /**
   * Close the <tt>Handler</tt> and free all associated resources.
   * This will also close the target <tt>Handler</tt>.
   *
   * @throws SecurityException if a security manager exists and if the caller does not have
   * <tt>LoggingPermission("control")</tt>.
   */
  @Override
  public void close() throws SecurityException {
    target.close();
    setLevel(Level.OFF);
  }

  /**
   * Set the <tt>pushLevel</tt>.  After a <tt>LogRecord</tt> is copied
   * into our internal buffer, if its level is greater than or equal to
   * the <tt>pushLevel</tt>, then <tt>push</tt> will be called.
   *
   * @param newLevel the new value of the <tt>pushLevel</tt>
   * @throws SecurityException if a security manager exists and if the caller does not have
   * <tt>LoggingPermission("control")</tt>.
   */
  public synchronized void setPushLevel(Level newLevel) throws SecurityException {
    if (newLevel == null) {
      throw new NullPointerException();
    }
    checkPermission();
    pushLevel = newLevel;
  }

  /**
   * Get the <tt>pushLevel</tt>.
   *
   * @return the value of the <tt>pushLevel</tt>
   */
  public Level getPushLevel() {
    return pushLevel;
  }

  /**
   * Check if this <tt>Handler</tt> would actually log a given
   * <tt>LogRecord</tt> into its internal buffer.
   * <p>
   * This method checks if the <tt>LogRecord</tt> has an appropriate level and
   * whether it satisfies any <tt>Filter</tt>.  However it does <b>not</b>
   * check whether the <tt>LogRecord</tt> would result in a "push" of the
   * buffer contents. It will return false if the <tt>LogRecord</tt> is null.
   * <p>
   *
   * @param record a <tt>LogRecord</tt>
   * @return true if the <tt>LogRecord</tt> would be logged.
   */
  @Override
  public boolean isLoggable(LogRecord record) {
    return super.isLoggable(record);
  }
}
